A study on photodegradation of polymers catalyzed by semiconductor

本研究分为两个部分；(1)固体聚合物（聚氯乙烯PVC）和水溶性聚合物（PEG和PVA）的光氧化(2)生物聚合物如DNA、RNA、碱基和多氨基酸的光氧化。(1)在二氧化钛或氧化锌悬浮液中，在紫外线照射和/或太阳照射下，研究了聚氯乙烯固体颗粒和聚氯乙烯薄膜的光催化氧化分解。对脱氯和二氧化碳的演化进行了监测，后者是通过乙酸和甲酸的中间体发生的。在tio_2 -水介质中加入过氧化氢和过硫酸钾等氧化剂，可促进聚合物样品的光降解。这些颗粒的光腐蚀也被扫描电子显微镜检查。PEG和PVA的水溶性聚合物也通过羟基和/或醛光降解为CH_3COOH、HCOOH和CO_2气体。(2)在物理防晒剂TiO_2锐钛矿/金红石颗粒存在的情况下，研究了DNA和RNA在UV-A和UV-B辐射下的敏化光化学，以评估这种防晒剂与这些底物接触时可能造成的损害。这两个核苷酸部分分解为二氧化碳，氮转化为氨和硝酸盐离子。通过透射电镜（TEM）、扫描电镜（SEM）和凝胶渗透色谱（gel - penetration chromatography）证实了DNA的物理和化学损伤。此外，还研究了氮在各种氨基酸中的归宿，作为一项基础研究。氨基酸中的氮主要转化为NH_4^+，少量转化为NO_3^-离子。

The research is composed of two sections ; (1) Photooxidation of solid polymers (polyvinylchloride PVC) and water-soluble polymers (PEG and PVA) (2) Photooxidation of biopolymers such as DNA,RNA,bases and polyamino acids.(1) The photocatalyzed oxidative decompositions of solid particles of PVC and a PVC film have been examined in suspensions of titania or zinc oxide illuminated by UV light and/or by solar exposure. Dechlorination and evolution of carbon dioxide were monitored, the latter occurring by the intermediacy of acetic and formic acids. The photodegradation of polymer specimens was enhanced in TiO_2-water media by such added oxidants as hydrogen peroxide and potassium persulfate. Photocorrosion of these particulates was also examined by scanning electron microscopy. Water-soluble polymers of PEG and PVA were also photodegraded to CH_3COOH,HCOOH and CO_2 gas via hydroxyl and/or aldehydes.(2) The sensitized photochemistry of DNA and RNA has been examined under UV-A and UV-B radiation in the presence of a physical sunscreen agent, TiO_2 anatase/rutile particles, to assess the possible damage that such an agent might cause on contact with such substrates. These two nucleotides are partially decomposed to carbon dioxide and the nitrogen are converted to ammonia and nitrate ions. The physical and chemical damage done to DNA was confirmed by TEM and SEM,and gel permeation chromatography. In addition, the fate of nitrogen in various amino acids was also examined as a fundamental research. The nitrogen in the amino acids are photoconverted predominantly into NH_4^+ and to a lesser extent into NO_3^- ions.